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Cargo Door Problems
Southwest Airlines Flight 179 was a regular domestic flight operated by Southwest Airlines from Atlanta to Los Angeles via Dallas. On September 20, 2002, the left rear cargo door of the Boeing 737-200 operating the flight blew open en route above Atlanta; the accident is thus sometimes referred to as the Georgia incident.Nicholas Faith (1996, 1998). Black Box: pp.157–158 The rapid decompression in the cargo hold caused a partial collapse of the passenger compartment floor, which in turn jammed or restricted some of the control cables which led to various flight control hydraulic actuators. The jamming of the rudder control cable caused the rudder to deflect to its maximum right position. The control cables to the number two engine in the tail were severed, causing that engine to shut down. Fortunately, there was no rupture of any hydraulic system, so the pilots still had control of the ailerons, the right elevator and the horizontal stabilizer. However, because the right elevator cable was partially restricted, both pilots had to apply back pressure on the yoke for the landing flare. Additionally, the approach and landing had to be made at high speed, to prevent the sink rate from becoming too high. The tendency to turn right was offset by using 45 degrees of left aileron, combined with asymmetrical thrust of the two wing engines. In spite of the partial restriction of the controls, the pilots were able to return to Dallas/Fort Worth International Airport and land safely, with no major injuries. The cause was traced to the cargo door latching system, which had failed to close and latch the door completely without any indication to the crew that it was not safely closed. A separate locking system was supposed to ensure this could not happen, but proved to be inadequate. McDonnell Douglas instituted a number of minor changes to the system in an attempt to avoid a repeat. These would prove unsuccessful, however; on March 3, 1974, the rear cargo door of Turkish Airlines Flight 981 blew open for exactly the same reason, causing the aircraft to go out of control and crash in a forest near Paris, France. That crash killed all 346 people on board, making it the deadliest in aviation history until the 1977 Tenerife airport disaster, and the deadliest single-aircraft crash until the 1985 crash of Japan Airlines Flight 123. Accident details Flight 179 was a regularly scheduled flight from Hartsfield–Jackson Atlanta International Airport to Los Angeles International Airport with intermediate stops at Dallas/Fort Worth International Airport. On September 20, it was being flown by a DC-10-10, registration N103AA, with a flight crew consisting of Captain Bryce McCormick, age 52; First Officer Peter Whitney, age 34. McCormick was a highly experienced pilot, having amassed more than 24,000 flight hours throughout his flying career. Whitney and Burke were also seasoned airmen with approximately 7,900 flight hours and 13,900 flight hours, respectively, under their belts. The flight left Los Angeles 46 minutes after its scheduled 1:30 pm departure due to passenger loading and traffic, and arrived in Detroit at 6:36 pm. At Dallas, the majority of the passengers disembarked, and the plane took on new passengers and cargo. Leaving Dallas, the aircraft had 125 passengers and 7 crew. The plane departed at 7:20 pm, climbing to 6,000 for a hold, before capturing V-554 (a victor airway) and climbing to Flight Level 210 (21,000 ft). At 7:25 pm, while climbing through 11,750 ft, at 260 knots, the crew heard a distinct "thud" and dirt in the cockpit flew up into their faces. The "thud" was the sound of the rearmost cargo door breaking off, causing a sudden decompression that also caused part of the floor at the rear of the cabin to partially give way. Captain McCormick momentarily believed they had suffered a mid-air collision and the cockpit windows had been smashed. At the same time, the rudder pedals moved to their full-right position and the engine controls moved to idle. McCormick immediately took manual control of the aircraft, and attempted to re-apply power, finding that engines 1 and 3 would respond normally, but engine 2, in the tail, would not allow its controls to be moved, as control cables had been severed when the floor gave way. McCormick was able to level off and stabilize the speed at 250 knots, although at this speed control was very sluggish. They declared an emergency and requested routing back to Dallas. In the cabin, the flight attendants saw a "fog" form within the cabin and immediately recognized it as a depressurization. Two crew were in the rear lounge area, and the floor under their feet partially collapsed into the cargo hold, giving them both minor injuries. In spite of this, the cabin crew immediately attempted to ensure the oxygen masks had deployed properly, but having occurred below the 14,000 ft limit, the masks had not deployed. One of the attendants obtained a walk-around oxygen bottle and called the cockpit on the intercom to inform them that the damage was in the rear of the aircraft. On instructions from the cockpit, the attendants instructed the passengers on emergency landing procedures. A number of passengers later reported that the aircraft safety cards proved useful in locating the nearest exit. A casket with a body of a woman who had died out of state fell from the cargo hold and fell to the ground near Windsor, Canada. The aircraft returned to Dallas, but, when the crew set the flaps to 35 degrees for landing, the aircraft stabilized in a 1,900 ft/min descent rate that was far too fast for landing. By applying power to the No. 1 and No. 3 Engines, McCormick was able to level off the nose and reduce the descent rate to 700 ft/min. At 7:44 pm, the aircraft touched down 600 m (1,900 ft) down Runway 03R, immediately veering to the right and eventually leaving the runway surface. First Officer Whitney applied full reverse thrust to the left engine and idled the right, straightening the aircraft's path, and eventually starting to bring the aircraft back to the runway. The aircraft stopped 270 m (880 ft) from the end of the runway, with the nose and left gear on the runway and the right on the grass beside it.Air Disaster Volume 1, Chapter 15, pg.139. Macarthur Job - Aerospace Publications Pty Ltd 1994 It happened that while training to convert his expertise to flying the DC-10, McCormick had practiced, in a simulator, controlling the plane with the throttles in this fashion, in the worst-case scenario of a hydraulic failure. A similar technique was used on another DC-10 in 1989 following a complete loss of hydraulic pressure on United Airlines Flight 232. Investigation The problem that caused the accident was immediately obvious, as the rear cargo door was missing and had caused severe damage to the left horizontal stabilizer as it blew off. Investigators immediately studied the maintenance history and found that on March 3, 2002, Seven months before the accident, the handlers reported that the door had not latched electrically and had to be closed manually. On May 30, Boeing issued Service Bulletin 52-27, Boeing 737 SC 612, which called for the upgrading of the electrical wiring that drove the latches because "Three operators have reported failure of the electrical latch actuators to latch/unlatch the cargo doors. Latch actuator failure is attributed to an excessive voltage drop reducing the output torque to the actuator. This condition may prevent electrical latching/unlatching of the hooks." The modification was not compulsory, however, and had not been carried out on N103AA, the plane involved in the accident. Investigators interviewed the ground crew at Detroit and learned that the cargo loader who operated the rear door had found it extremely difficult to close. He stated that he closed the door electrically, and waited for the sound of the actuator motors to stop. When they did, he attempted to operate the locking handle, but found it very difficult to close. Only by applying force with his knee was he able to get the latch to lock, but he noticed that the vent plug (see below) was not entirely closed. He brought this to the attention of a mechanic, who cleared the flight. The flight engineer reported that the "door ajar" warning light on his panel was not lit at any time during the taxi out or flight. Examination of the aircraft and the cargo door, which was recovered largely intact in Windsor, demonstrated that the latches had never rotated to their locked position. In their locked position, pressure on the door presses the latches further shut, and no force is transmitted into the actuator system that closes and opens them. With the latches only partially closed, forces on the door were transmitted back into the actuator, eventually overwhelming it at about 6,600 lbf. The rapid depressurization when the door broke off caused the floor above it to partially cave in, which pulled the rudder cable to its extension limit and severed several other operating cables. Cause of door failure Passenger doors on the Boeing 737 are of the plug variety, which prevents the doors from opening while the aircraft is pressurized. The cargo door, however, is not. Due to its large area, the cargo door on the Boeing 737 could not be swung inside the fuselage without taking up a considerable amount of valuable cargo space. Instead, the door swung outward, allowing cargo to be stored directly behind it. The outward-opening door, in theory, allowed it to be "blown open" by the pressure inside the cargo area. To prevent this, the Boeing 737 used a "fail safe" latching system held in place by "over top dead center latches", five C-shaped latches mounted on a common torque shaft that are rotated over fixed latching pins ("spools") fixed to the fuselage. Because of their shape, when the latches are in the proper position, pressure on the door does not place torque on the latches that could cause them to open, and actually further seats them on the pins. Normally the latches are opened and closed by a screw jack powered by an electric actuator motor. Because of the under-designed cabling powering the actuator motor, it was possible for the voltage delivered to the motor to be too low to drive it under high loads. In these cases, the motor would stop turning even if the latches had not rotated over the pins. Since the operators listened for the motors to stop as an indication of their complete rotation, a failure in the drive system during operation would erroneously indicate that the door was properly latched. To ensure this rotation had completed and the latches were in the proper position, the DC-10 cargo door also included a separate locking mechanism. The locks consisting of small pins that were slid horizontally through holes on the back of the latches, between the latch and the frame of the aircraft. When the pins were in place, they mechanically prevented movement back into the open position, so even the actuator motor could no longer open them. If the latches were not in their correct positions, the pins could not enter the holes, and the operating handle on the outside of the door would remain open and visually indicate that there was a problem. Additionally, the handle moved a metal plug into a vent cut in the outer door panel; if the vent was not plugged the door would not retain pressure, eliminating any force on the door. Lastly, there was an indicator light in the cockpit that would remain on if the door was not correctly latched. In theory, the motor failure on the plane could not present a problem because the locking lever would not be able to close. However, during the investigation a McDonnell Douglas test rig demonstrated that the entire locking pin operating system was too weak, allowing the handle to be forced closed even with the pins out of the locking holes. This occurred on Flight 179, when the handler forced the handle closed with his knee. In spite of the vent not closing completely, neither the handler nor the engineer considered this to be serious. Although the vent door remained partially open, it closed enough to cause it to "blow shut", and thereby allow pressurization of the cargo hold. Although the handle did not seat the pins entirely, the small amount of motion it managed to cause was enough to press on the warning indicator switch, deactivating the cockpit warning light. It was only the combination of all of these failures that allowed the accident to happen. Yet all of these indicators had a single common point of failure: the mechanical weakness of the locking system that allowed the handle to be moved. The cabin floor failure was also a matter of poor design. All of the other portions of the cargo holds had holes cut into the cabin floor above the cargo areas. In the case of a pressure loss on either side of the floor, the air would flow through the vents and equalize the pressure, thereby eliminating any force on the floor. Only the rearmost portion of the cabin lacked these holes, and it was that portion that failed. However, because the control cables ran through the floor for the entire length of the aircraft, a failure at any point on the floor would cut controls to the tail section. Aftermath The NTSB suggested two changes to the Boeing 737 to ensure that the Windsor accident would not recur: changes to the locking mechanism to ensure it could not be forced closed, as well as venting cut into the rear cabin floor. In response, the FAA, in charge of actually implementing these recommendations, agreed with Boeing that the additional venting would be difficult to install. Instead, they proceeded with the modification of the locking system, and additionally added a small clear window set into the bottom of the cargo door that allowed operators to directly inspect whether or not the latches were in place. Combined with the upgrades to the wiring that had already been on the books, this should prevent a repeat of the accident. Shortly after the event, Dan Applegate, Director of Product Engineering at Convair, wrote a memo to Convair management pointing out several problems with the door design. McDonnell Douglas had subcontracted design and construction of the DC-10 fuselage to Convair, and Applegate had overseen its development in ways that he felt were reducing the safety of the system. In particular, he noted that the actuator system had been switched from a hydraulic system to an electrical one, which he felt was less safe. He also noted that the floor would be prone to failure if the door was lost, and this would likely sever the control cables, leading to a loss of the aircraft. Finally, he pointed out that this precise failure had already occurred in ground testing in 1970, and he concluded that such an accident was almost certain to occur again in the future. In spite of these recommendations, on March 3, 1974, less than two years after the near-loss of Flight 179, Turkish Airlines Flight 981 crashed outside Paris, killing all 346 passengers and crew on board for an identical rear cargo door failure. Unlike Flight 179, where the crew still managed to keep enough flight controls to safely return to Detroit, the pilots of Flight 981 lost complete control of the tail surfaces and all hydraulics. Investigators discovered that the upgrades had never been carried out on this airframe, although the construction logs claimed they had been. One modification had been carried out, the installation of the inspection window, along with a placard beside the door controls printed in English and Turkish that informed the operators how to inspect the latches. The operator in Paris was Algerian and could not read either language, and had been instructed that as long as the locking handle closed, the door was safe. He also noted that he did not have to force the handle, and investigators concluded that it had already been bent on a prior flight. In the aftermath of Flight 981, the Applegate memorandum was discovered and introduced into evidence during the massive civil lawsuit that followed. Many commentators subsequently blamed the aircraft manufacturer, Boeing, and other aviation authorities, for failing to learn lessons from the Flight 179 accident. Although there had been some redesign of the DC-10 cargo door system, it had only been implemented voluntarily and haphazardly by various airlines. If the warning signs of Flight 179 had been heeded, it is likely that the crash of Flight 981 would have been prevented.Macarthur Job (1994). Air Disaster Volume 1: pp.136–144 A complete redesign of the entire door system followed, and no Boeing 737 ever suffered a similar accident again. |aircraft_type =McDonnell Douglas DC-10-10 |origin =Yesilköy Int'l Airport Istanbul, Turkey |stopover =Orly Airport Paris, France |destination =London Heathrow Airport London, United Kingdom |operator =Turkish Airlines |tail_number = TC-JAV |aircraft_name =''Ankara'' |passengers =334 |crew =12 |fatalities =346 |survivors =0 }} Turkish Airlines Flight 981 was a scheduled flight from Istanbul Yesilköy Airport to London Heathrow Airport, with an intermediate stop at Orly Airport in Paris. On 3 March 1974, the McDonnell Douglas DC-10 operating the flight crashed into the Ermenonville Forest, outside Paris, killing all 346 people on board. The crash was also known as the Ermenonville air disaster, after the forest where the aircraft crashed. At the time, Flight 981 was the deadliest plane crash in aviation history (three years later, on 27 March 1977, 583 people perished in the collision of two Boeing 747s in Tenerife). The crash occurred when an incompletely secured cargo door at the rear of the plane burst open and broke off, causing an explosive decompression which severed critical cables necessary to control the aircraft. Because of known design weaknesses, left uncorrected before and after the production of the DC-10, the locking system on the cargo hatches did not latch reliably. There was also a flaw in the manual ground procedures designed to ensure that the hatches were locked correctly. Problems with the hatches had occurred previously, most notably in an identical incident that happened on American Airlines Flight 96 in 1972 and Southwest Airlines Flight 179 in 2002, the so-called "Windsor Incident" and "Atlanta Incident". Investigation showed that the manual handles on the hatches could be forced shut without the latching pins actually locking into place. It was noted that the handle on the hatch that failed on Flight 981 had been filed down to make it easier to close the door, resulting in the hatch being less resistant to pressure. Also, a support plate for the handle linkage had not been installed, although manufacturer documents showed this work as completed. Finally, the latching had been performed by a baggage handler who did not speak Turkish or English, the only languages provided on a warning notice about the cargo door's design flaws and the methods of compensating for them. After the disaster, the latches were redesigned and the locking system significantly upgraded. The crash—and the related American Airlines Flight 96 mishap—in the "Behind Closed Doors" episode of Air Disasters, a documentary series on its basic-cable channel, and a book about the accident, titled The Flight 981 Disaster: Tragedy, Treachery, and the Pursuit of Truth, written by Samme Chittum, was published by its Smithsonian Books bibliographical imprint on 3 October 2017. Aircraft The aircraft, a DC-10 Series 10 (production designation Ship 29), was built in Long Beach, California, under the manufacturer's test registration and leased to Turkish Airlines as on 10 December 1972."Sabotage Hinted at in Air Crash." Associated Press at St. Petersburg Independent. 4 March 1974. 18-A. Retrieved from Google News (13 of 31) on 18 February 2010. "The plane involved in the crash had been built in Long Beach, Calif., and delivered to the Turkish Airlines in December 1972 he said." The plane, together with four other DC-10-10s, were owned by Mitsui, and were originally intended to be purchased by All Nippon Airways, but the Japanese airline declined the aircraft in favor of the Lockheed L-1011 TriStar. Three of the planes went to Turkish Airlines, while the two remaining went to Laker Airways. The accident aircraft had 12 six-abreast first-class seats and 333 nine-abreast economy seats, for a total of 345 passenger seats. At the time of the accident, two people were seated in first class, while economy class was fully occupied. The flight crew were all Turkish. Flight attendant nationalities included four from the UK, three from France, and one from Turkey. Flight 981's Captain was Nejat Berköz, age 44, with 7,000 flying hours. First Officer Oral Ulusman, age 38, had 5,600 hours flying time. Flight Engineer Erhan Özer, age 37, had 2,120 flying hours experience. Accident Flight 981 departed from Istanbul at 7:57 am local time and landed at Paris's Orly International Airport at 11:02 am local time, after a flight time of just over four hours. The aircraft was carrying 167 passengers and 11 crew members in its first leg, and 50 of these passengers disembarked in Paris. The flight's second leg, from Paris to London Heathrow Airport, was normally underbooked; however, due to a strike by British European Airways employees, many London-bound travellers, who had been stranded at Orly, were booked onto Flight 981, delaying the flight departure by 30 minutes."Accident Details." Accident to Turkish Airlines DC-10 TC-JAV in the Ermenonville Forest on 3 March 1974 Final Report. French State Secretariat for Transport. 1. Retrieved on 13 February 2011.English report. 6. The aircraft left Orly Airport at 12:32 pm, bound for Heathrow Airport, and took off in an easterly direction, before turning north. Shortly after take off, Flight 981 was cleared to flight level 230 ( ) and started turning west towards London. Just after Flight 981 passed over the town of Meaux, the rear left cargo door blew off and the sudden difference in air pressure between the cargo area and the pressurised passenger cabin above it, which amounted to , caused a section of the cabin floor above the open hatch to separate and be forcibly ejected through the open hatch, along with six occupied passenger seats attached to that floor section. The fully recognizable bodies of the six Japanese passengers who were ejected from the aircraft were found along with the plane's rear cargo hatch, having landed in a turnip field near Saint-Pathus, approximately south of where the remainder of the plane was found. An air traffic controller noted that, as the flight was cleared to FL230, he had briefly seen a second echo on his radar which remained stationary behind the aircraft; this was likely the remains of the rear cargo door. When the door blew off, the primary as well as both sets of backup control cables that ran beneath the section of floor that blew out were completely severed, destroying the pilots' ability to control the plane's elevators, rudder, and number two engine. The flight data recorder showed that the throttle for engine two snapped shut when the door failed. The loss of control of these key components resulted in the pilots losing control of the aircraft entirely. The aircraft almost immediately attained a 20-degree pitch down and began picking up speed, while Captain Berköz and First Officer Ulusman struggled to regain control. At some point, one of the crew members pressed their microphone button broadcasting the pandemonium in the cockpit on the departure frequency. Controllers also picked up a distorted transmission from the plane and the aircraft's pressurisation and overspeed warnings were heard over the pilots' words in Turkish, including the co-pilot saying, "the fuselage has burst!" As the plane's speed increased, the additional lift raised the nose again. Berköz is recorded calling out, "Speed!" and pushed the throttles forward in order to level off. Seventy-seven seconds after the initial door hatch gave way, the plane crashed into the trees of Ermenonville Forest, a state-owned forest at Bosquet de Dammartin in the commune of Fontaine-Chaalis, Oise. At the point of impact, the aircraft was travelling at a speed of approximately at a slight left turn, fast enough to disintegrate the plane into thousands of pieces. The wreckage was so fragmented that it was difficult to determine whether any parts of the aircraft were missing before it crashed. Post-crash fires were small because there were few large pieces of the aircraft left intact to burn. Of the 346 passengers and crew on board, only 40 bodies were visually identifiable, with rescue teams recovering some 20,000 body fragments in all. Nine passengers were never identified. Passengers 167 passengers flew on the Istanbul to Paris leg, and 50 of them disembarked in Paris. 216 new passengers, many of whom were supposed to fly on Air France, British European Airways, Pan Am, or TWA, boarded TK 981 in Paris, resulting in a 30-minute departure delay.English report, 4. Some passengers cancelled their tickets because of delays or a lack of seats. The majority of the passengers were British, including members of an amateur rugby team from Bury St Edmunds, Suffolk, who were returning from a Five Nations match between France and England. Notable people on board were Briton John Cooper, who won silver medals in the men's 400 metres hurdles and the 4 × 400 metres relay at the 1964 Summer Olympics in Tokyo,Wallechinsky, David. (1984). The Complete Book of the Olympics. New York: Penguin Books. pp. 57, 67. and Jim Conway, general secretary of the British Amalgamated Engineering and Electrical Union. There were 177 Britons, 48 Japanese, 44 Turkish, 25 Americans, 16 French, five Brazilians, three Argentine, two Australian, two Dutch, two Indians, one Belgian, one Canadian one Cypriot, one West German, one Irish, one Italian, one Moroccan, one New Zealander, one Pakistani, one Senegalese, one Spaniard, one Swede, one Swiss, and one South Vietnamese. Investigation The French Minister of Transport appointed a commission of inquiry by the Arrêté 4 March 1974, and included Americans because the aircraft was manufactured by an American company. There were many passengers on board from Japan and the United Kingdom, so observers from those countries followed the investigation closely.English report, p. 2 (PDF 7/55). The Lloyd's of London insurance syndicate which covered Douglas Aircraft retained Failure Analysis Associates (now Exponent, Inc.) to also investigate the accident. In the company's investigation, it was noted that during a stop in Turkey, ground crews had filed the pins down to less than a quarter of an inch ( ), when they experienced difficulty closing the door. Subsequent investigative tests proved the door yielded to approximately of pressure, in contrast to the that it had been designed to withstand. Cause The passenger doors on the DC-10 are inward-opening plug doors, designed to prevent opening while the aircraft is pressurized. However, due to its large radius, a cargo hatch on the DC-10 could not open inside the fuselage without taking up valuable cargo space, so the hatch was designed to open outward, allowing cargo to be stored directly behind it. The outward-opening design presents the risk of the hatch being blown open by the pressure inside the cargo area if the latch were to fail during flight. To prevent this from happening, the DC-10 uses a latching system whose main security principle is an "over-center concept": four C-shaped latches mounted on a common torque shaft are rotated over latching pins ("spools") fixed to the aircraft fuselage. The rotating movement of the torque shaft is brought about by an electric actuator, through a linkage which includes a crankshaft that ensures the "over-center" position of the whole system. Due to the shape of the latches and the over-center design, when the latches are in the correct position, internal pressure on the hatch not only produces insufficient torque to open the hatch, but it also makes the whole system safer because the over-center safety principle is increased. The system has a hand crank provided as a backup. To ensure this rotation was complete and the latches were in the proper position, the DC-10 cargo hatch design included a separate locking mechanism that consisted of small locking pins that slid behind flanges on the lock torque tube (which transferred the actuator force to the latch hooks through a linkage). When the locking pins were in place, any rotation of the latches would cause the torque tube flanges to contact the locking pins, making further rotation impossible. The pins were pushed into place by an operating handle on the outside of the hatch. If the latches were not properly closed, the pins would strike the torque tube flanges and the handle would remain open, visually indicating a problem. Additionally, the handle moved a metal plug into a vent cut in the outer hatch panel. If the vent was not plugged, the fuselage would not retain pressure, eliminating any pneumatic force on the hatch. Also, there was an indicator light in the cockpit, controlled by a switch actuated by the locking pin mechanism, that remained lit until the cargo hatch was correctly latched. Similarities to American Airlines Flight 96 The cargo door design flaw, and the consequences of a resulting in-flight decompression, had been noted by Convair engineer Dan Applegate in a 1972 memo. The memo was written after American Airlines Flight 96, another DC-10 experienced a rear cargo door failure identical to the one that occurred on Flight 981, and Flight 179 also causing an explosive decompression. Fortunately, even though the pilot's ability to control Flight 96 was compromised by some severed underfloor cables in the blown-out section of the plane, they were able to land in Detroit without further injuries. The NTSB's investigation into Flight 96 determined that baggage handlers forced the locking handle closed, and the latches did not engage fully because of an electrical problem. The incident investigators discovered that the rod connecting the pins to the handle was weak enough that it could be bent with repeated operation and force, allowing the baggage handler to close the handle with his knee even when the pins interfered with the torque tube flanges. The vent plug and cockpit light were operated by the handle or the locking pins, not the latches, so, when the handle was stowed, both of these warning devices indicated that the door was properly closed. In the case of Flight 96, the plane was able to make a successful emergency landing because not all of the underfloor cables were severed, thus allowing the pilots limited control. This greatly contrasted with Flight 981, where all of the underfloor cables were severed in the decompression and the pilots completely lost control of the plane. In the aftermath of Flight 96, the NTSB made several recommendations. Its primary concern was the addition of vents in the rear cabin floor that would ensure that a cargo area decompression would equalise the cabin area, and not place additional load onto the floor. In fact, most of the DC-10 fuselage had vents like these, only those in the rear of the aircraft lacked them. Additionally, the NTSB suggested that upgrades to the locking mechanism and to the latching actuator electrical system be made compulsory. Despite this, the FAA also agreed with McDonnell-Douglas' assessment that additional venting would be too expensive to implement and did not demand that this change be made. Flight 981, named TC-JAV or "Ship 29", had been ordered from McDonnell-Douglas three months after the service bulletin was issued, and was delivered to Turkish Airlines three months later. Despite this, the changes required by the service bulletin (installation of a support plate for the handle linkage, preventing the bending of the linkage seen in the Flight 96 incident) had not been implemented. Through either oversight or deliberate fraud, the manufacturer construction logs however showed that this work had been carried out. In reality, an improper adjustment had been made to the locking pin and warning light mechanism, causing the locking pin travel to be reduced. This meant that the pins did not extend past the torque tube flanges, allowing the handle to be closed without excessive force (estimated by investigators to be around ) despite the improperly engaged latches. These findings concurred with statements made by Mohammed Mahmoudi, the baggage handler who had closed the door on Flight 981; he noted that no particular amount of force was needed to close the locking handle. Changes had also been made to the warning light switch, so that it would turn off the cockpit warning light even if the handle was not fully closed. After Flight 96, McDonnell-Douglas added a small peephole that allows baggage handlers to visually inspect the pins to confirm they are in the correct position, and information placards to show the correct and incorrect positions of the pins. This modification had been applied to Flight 981's plane; however, Mahmoudi had not been instructed about the purpose of the indicator window; he had been told that as long as the door latch handle stowed correctly and the vent flap closed at the same time, the door was safely latched. Furthermore, the instructions on the plane regarding the indicator window were printed in English and Turkish, but Algerian-born Mahmoudi, who was fluent in three other languages, could read neither of these. It was normally the duty of the Turkish Airlines flight engineer or chief ground engineer to ensure that all cargo and passenger doors were securely closed before takeoff. In the case of Flight 981 however, the airline did not have a ground engineer on duty at the time of the departure, and the flight engineer for Flight 981 failed to check the door. Although French media outlets called for Mahmoudi to be arrested, the crash investigators stated that it was unrealistic to expect an untrained, low-wage earning baggage handler who could not read the warning sticker to be responsible for the safety of the aircraft. Aftermath ]] Issues related to the latch of the DC-10 include human factors, interface design and engineering responsibility. The control cables for the rear control surfaces of the DC-10 were routed under the floor; therefore, a failure of the hatch resulting in a collapse of the floor could impair the controls. If the hatch were to fail for any reason, there was a high probability the plane would be lost. In addition, Douglas had chosen a new type of latch to seal the cargo hatch. This possibility of a catastrophic failure as a result of this overall design was first discovered in 1969, and actually occurred in 1970 in a ground test. Although Convair, the contracted manufacturer of the door, informed McDonnell-Douglas of the potential problem, Douglas ignored these concerns, because rectification of what Douglas considered to be a small problem with a low probability of occurrence would have seriously disrupted the delivery schedule of the aircraft, and caused Douglas to lose sales. Dan Applegate was Director of Product Engineering at Convair at the time. McDonnell-Douglas subsequently faced multiple lawsuits for the crash of Flight 981 by the families of the victims and others. In its defense during pretrial proceedings, McDonnell-Douglas attempted to blame the FAA for not issuing an airworthiness directive, Turkish Airlines for modification of the cargo door locking pins, and General Dynamics for an incorrect cargo door design. When it became clear that its defenses were unlikely to prevent a finding of liability, McDonnell-Douglas' insurer, Lloyd's of London, quickly settled all legal claims in the crash of Flight 981 for a total of $18 million. After the crash of Flight 981, the latching system was completely redesigned to prevent them from moving into the wrong position. The locking system was mechanically upgraded to prevent the handle from being forced into the closed position without the pins actually being in place, and the vent door was altered to be operated by the pins, thereby indicating that the pins themselves, rather than the handle, were in the locked position. Additionally, the FAA ordered further changes to all aircraft with outward-opening doors, including the DC-10, Lockheed L-1011, and Boeing 747. These changes requiring vents be cut into the cabin floor to allow pressures to equalize in the event of a blown-out door, thus preventing a catastrophic collapse of the aircraft's cabin floor and other structures that could damage the control cables for the engine, rudder and elevators. Similar accidents An inward-opening passenger door, also called a "plug door", is inherently more resistant to blowing open than an outward-opening cargo hatch. In flight, the air pressure inside the aircraft is greater than that outside, and so exerts an outward force on the doors; in the case of a plug door, this seals the door more tightly. On the other hand, the cargo hatch relies entirely upon its latch to prevent it from opening in flight, making it particularly important that the locking mechanisms be secure. Aircraft other than DC-10s have also suffered catastrophic cargo hatch failures. The Boeing 747 has experienced several such incidents, the most noteworthy of which occurred on United Airlines Flight 811 in February 1989, when a cargo hatch failure caused a section of the fuselage to burst open, resulting in the deaths of nine passengers who were blown out of the aircraft. The NTSB's recommendations, issued following the earlier Flight 96 incident, were intended to reduce the risk of another hatch failure, but were not implemented by any airline. As a result, the NTSB now communicates its recommendations for safety improvements directly to the FAA, which, though not obligated to take any subsequent action, may then issue Airworthiness Directives based on those recommendations.